Effect of seed weight on height growth of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) seedlings in a nursery

Abstract

Different mean seed weights were produced within each of 10 young Douglas-fir trees by leaving some developing cones unbagged and enclosing others in Kraft paper bags for two different durations. On the average, 10 days in the bag increased filled-seed weight by about 1%. Unbagged cones and cones from the 117-day bagging duration were wind pollinated. Seeds from these cones were, therefore, of comparable genetic makeup and were used in further nursery growth tests. To eliminate the effect of germination rate or time, samples of filled seeds from each treatment on each parent tree were sown as germinant seedlings on one date. Cotyledon number was counted and 1st-year epicotyl lengths and 2nd-year total heights were measured on all seedlings. Seedling volumes were estimated by assuming diameters were proportional to heights. On the average, bagging cones for 117 days increased seed weight by 10.7%, 1st-year epicotyl length by 9.1%, and 2-year total height by 4.0%. All differences were statistically significant. Results were compared with other reports of the relations between seed weight and growth and reasons for inconsistencies were discussed. Size differences were projected to later ages with a growth model and practical implications of long-term seed effects on plant size, of increasing seed size through cultural techniques, and of grading seed lots by size were considered.